I have checked they up in my dictionaries and I have found out that their definitions are the same.
However, what I have realized is that relation is rather impersonal while relaitonship is more personal.
Do you concur with me on that?
You can have a relationship with somebody.
You can't have a relation with somebody.
You can have relationships with several people.
You can have (sexual) relations with one person.
You can have (sexual) relations with several people.